1. Field of the Invention
The present invention relates to a triple-port video memory system provided with both a single random access memory (referred to as RAM, hereinafter) and two serial access memories (referred to as SAMs, hereinafter), and more specifically to a video memory system suitable for use with a system for displaying a plurality of pictures in windows in particular when serial image data obtained by a camera are displayed on a display unit.
2. Description of the Background Art
Multimedia have come public notice as auxiliary means for intellectual activity. In the multimedia, the technique related to image data composed of a great quantity of information is particularly important. That is, the important technique is to transmit information effectively by processing and displaying motion picture or by displaying both motion picture and motionless picture on the same display screen. In the field of the processing and displaying the motion picture, the video memory is extremely important from the standpoint of the data processing.
In general, image data are outputted from a camera in series and further inputted to a display unit also in series with respect to time. Therefore, as far as the image data obtained by a camera are simply displayed, no specific functions are required for the video memory. That is, the ordinary video memory can be used as it is, which can store inputted data and output the stored data simply.
However, when image data are required to be processed, a special video memory is necessary which can access the stored image data at random and further can rewrite the image data freely. Since data are outputted from the camera continuously, the triple-port video memory (triple-port VRAM) provided with both an input serial port and an output serial port (to the display unit) is suitable for processing the motion picture.
FIG. 11 is an illustration for assistance in explaining the concept of the triple-port video RAM (VRAM) so far proposed. In FIG. 11, two SAMs (SAMA and SAMB) are arranged for one RAM, and each of these SAMA, RAM and SAMB can be operated perfectly independently. However, a split transfer method is adopted to data transfer between the SAMA and RAM and data transfer between the RAM and the SAMB, respectively. Further, during the data transfer, the access to the RAM is limited. As is well known, in this split transfer method, the memory is split into some split sections, and data are transferred for each split memory section. To realize the split data transfer as described above, each memory section is split into a lower portion L and an upper portion U.
The image data transfer operation of the triple-port video RAM (VRAM) shown in FIG. 11 will be described hereinbelow.
Image data outputted from a camera 20 are inputted in sequence and in series from the lower portion L to the upper portion U of the SAMA. When the data are being inputted to the upper portion U of the SAMA, data in the lower portion L of the SAMA are transferred to one row 1 of the RAM, for instance. Further, in the same way, the data are written to rows 2 and 3 of the RAM in sequence. The data stored in the RAM are accessed at random and processed (e.g., a part of data are rewritten) before transferred to the SAMB. After that, data stored in the row 1 of the RAM are transferred to the lower portion L of the SAMB. When the data are being outputted to a display 30 in series, data in the SAMBL portion are transferred to the SAMBU portion, and the data in the RAM are transferred to the upper portion U of the SAMB, so that the data in the rows 2 and 3 of the RAM are transmitted in sequence to the display 30.
In the case of the motion picture, since the image data are not interrupted, the time during which data can be processed is the time interval during which data are stored in the RAM. Accordingly, the data processing time is proportional to the memory capacity of the RAM. As described above, the data values in the RAM always change due to the data transfer to the SAMB and the data rewrite in the RAM itself.
FIG. 12 is an illustration for assistance in explaining the operation the case where an inserted picture (whose data are different from the data of the background picture) is displayed on a part (i.e., a window 31) on the display picture 30. In FIG. 12, only two SAMs and a RAM are shown. Further, in practice, pixel data arranged along a single horizontal scanning line S (crossing the window 31 in FIG. 13) are stored in a plurality of VRAMs separately and therefore the pixel data are processed as discrete data from the respective SAMs. In this example, however, the explanation will be made by assuming that data are given from the SAM of one VRAM for brevity.
In this case, as shown in FIG. 12, if the row 3 of the RAM corresponds to the scanning line S, the data values in the row 3 of the RAM are rewritten before being transferred to the SAMB to obtain any required display. However, when the data existing between two addresses (a) and (b) in correspondence to the window width ends A and B are fixed data such as letter data, since the data must be always rewritten, such data processing is not effective.
Under due consideration of these situations, in order to execute the image data processing efficiently, it is possible to define a predetermined area of the RAM as a fixed area and not to transfer the image data of the camera to this fixed area.
FIG. 14 shows this method. For instance, fixed data are stored in an area of serial rows including the row 4, and data are transferred from the SAM to the area other than the fixed area. In this method, however, when the fixed data structure must be changed at the positions determined by A and B on the display shown in FIG. 13 or when this window area must be moved freely to another position on the display, a complicated data processing is required.
This will be explained in further detail with reference to FIGS. 15 to 18. In these drawings, although only the RAM is shown, in the same way as with the cases shown in FIGS. 11, 12 and 14, the assumption is made that each of the SAMs is split into the upper (U) portion and the lower (L) portion, and further the upper and lower portions of the RAM correspond one-to-one to the upper and lower portions of the SAMs. Further, since the split transfer method is adopted, in the SAMs, it is possible to set the head position of the serial access and the final position of-the serial access at which the split upper and lower portions of the SAM are switched. First, in FIG. 15, as shown by arrows, data are accessed in series via the SAM to the column address (a) in the row 1 to obtain the background data. During this serial access, data are transferred from the row 4 of the fixed data area of the RAM to the U portion of the SAM for instance and further these transferred data are accessed in series. By doing this, it is possible to display an inserted picture composed of fixed data. In this method, however, although data must be next accessed beginning from the address (b) in the row 1 of the RAM, since data in this area can be transferred to only the U portion of the SAM, there exists such a problem in that it is impossible to connect data of the background to data of an inserted picture being accessed in series at the U portion. This problem can be solved by arranging fixed data appropriately so as to correspond to the addresses (a) and (b), as shown in FIG. 16. In FIG. 16, fixed data are so arranged that when the data are being serial accessed from the address (a) to the address (b), the serial access is shifted from the U portion to the L portion and further that when the serial access begins from the address (a) and reaches the upper end, the serial access is changed beginning from the address (0) to the address (b). By arranging the fixed data as described above, it is possible to shift the serial access to the background data beginning from the address (b), so that the problem as explained with reference to FIG. 15 can be solved.
Here, under the conditions that the data are arranged as described above, when the position of the inserted picture is moved on the display, a problem arises. This will be explained with reference to FIG. 17.
FIG. 17 shows the case where the area of the inserted picture data area is perfectly included in the data area of the L portion. In this case, when the fixed data arrangement the same as with the case shown in FIG. 16 is adopted, at the address (b) at which the inserted picture display is switched to the background display, there arises a problem in that data must be transferred from the RAM to the SAM on the side where the serial access is being made. To overcome this problem, as shown in FIG. 18, it is necessary to rearrange the fixed data so that the data transfer is not required from the RAM to the SAM on the side where the serial access is being made. In addition, in spite of the fact that it is ideal that both the inserted picture data and the background data can be arranged at predetermined positions irrespective of the inserted picture position on the display, this ideal arrangement cannot be attained in the prior art video memory system.
As described above, in the prior art video memory systems, the data arrangement of inserted picture must be finely corrected according to the position and the size of the inserted picture relative to the background, with the result that there exists a problem in that a high data processing efficiency cannot be attained, in spite of the fact that the data area of inserted picture and the data area of the background picture are arranged separately from each other in the RAM.